The retreating or recapping of tires with a pre-cured tread is a widely practiced art. Typically, a tire casing to be processed is prepared by grinding or buffing off any old tread remaining on the casing. In one process, cement is then applied and a layer of uncured cushion stock is applied to the cemented casing. An additional layer of cement is applied over the uncured cushion stock and a pre-cured tread layer is then applied over the cushion stock. Finally, the entire composite uncured retread is inserted into a rubber curing envelope and the encased retread is then placed into a curing chamber or module, typically at a temperature of 200.degree. to 325.degree. F. and typically at a pressure of 50 to 150 pounds per square inch. The curing envelope functions as a protective covering to prevent air and/or steam used during the curing process from coming into contact with the cement and uncured cushion stock during the curing process. A further function of the curing envelope is to compress the various components described above into tight engagement with the casing so that a suitable product is produced during the curing operation. Following the curing process, the encased retread is removed from the curing chamber and the curing envelope is removed to provide the finished retread.
A common practice has been to cure the green rubber curing envelopes in unique molds used solely for this purpose. An attendant disadvantage is the procurement cost of these special purpose molds. Presti U.S. Pat. No. 4,036,271 shows a press wherein a seamless curing envelope is compression formed from an uncured elastomeric slug.
In an effort to avoid the drawbacks and disadvantages of prior an techniques for producing curing envelopes, Perdue U.S. Pat. No. 4,836,877 proposes a process wherein an elastomeric material is extruded in substantially tubular form, with portions of the wall thickness of the circumference of the extruded tubing being of a thickness substantially greater than the wall thickness of the remainder of the tubing. A length of the extruded tubing is cut from the elongated tubing issuing from the extruder and is butt-seamed to form an annular tube substantially of circular cross-section. The tube is then cured in a curing mold of the type used for curing conventional automobile or truck tubes, except that the cavity of the mold is given the cross-sectional shape corresponding to the desired cross-sectional shape of the curing envelope. The cured annular tube is then slit to open up the annular tube and, optionally, portions of the radially inner wall of the tube may be removed to provide a finished curing envelope of desired size.